ARM: dts: exynos: remove Exynos4212 support (dead code)

There are no Exynos4212 based boards in mainline, so there is no need to
keep additional files for SoCs, which are never used. This patch removes
support for Exynos4212 SoCs and moves previously shared Exynos4412
definitions to a single file to simplify future maintenance.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>